As I mentioned in a previous blog, GPR systems work by sending or transmitting a pulse of energy into the host material under investigation and recording the reflected or return signal. This return signal contains information such as signal strength and reflection events in the signal stream. Multiple pulses of energy are used to create data profiles or scans and a reflection event is produced when the transmitted pulse of energy comes into contact with other materials of differing electrical properties to the host. These other materials can reflect and/or absorb some of the energy pulse and differing electrical properties or Relative Dieletric Permittivity create contrasts in the data as the amplitude of the reflection varies due to this factor. GPR systems convert the return signal to a digital format and record it to the system hard drive where it can be accessed for display purposes and to perform post-processing tasks.
To ensure that we can do the data thing, we have to get the basics right.
- Keep an eye on the weather. Most people have a mobile phone; use the weather app to see what the weather’s going to do while you are on site. Rain will affect your results as it will change the properties of the ground - remember this!
- Make sure the system’s batteries are charged enough to complete the survey; carry spares if you can. Have a backup PC too, if the system runs with a regular tablet or PC.
- Make sure any connecting cables are good and not damaged. If the system communicates with a cable between antenna and computer, then carry a spare.
- If the system has pneumatic tyres, make sure they are the correct pressure. This will ensure that the rolling circumference is correct for the encoder wheel calibration settings.
- Set the encoding wheel calibration to the actual site you are working on. It only takes two minutes; a simple step but can eliminate any linear drift in measurements.
- Look around your site - plan ahead if your collecting in grids, make notes, take site photos.
We haven’t got the system up and running, yet, so join me next time look at the system.